Science -- Your Future, Scotland's Future
SCI-FUN Roadshow Exhibits -- Sink or Swim?
SCI-FUN Roadshow Exhibits -- Sink or Swim?
SCI-FUN Roadshow Exhibits -- Sink or Swim? Supplement
In this exhibit you learn about density.

Whether or not things float depends on their density. We can work out density from an object's mass and volume:

density = mass / volume

Pure water has a density of 1. That means that 1 L of water weighs 1 kg. A litre of air would weigh next to nothing, so it has a density much less than 1.

In this exhibit you see that the sugar-free Irn Bru floats and the normal Irn Bru sinks. Anything with a density of 1 or less will float in water, and anything with a density of more than 1 will sink.

In fact, normal Irn Bru has a density of 1.05 and sugar-free Irn Bru has a density of 1. The difference in density is because normal Irn Bru contains sugar. The artifical sweetener used in the sugar-free Irn Bru is much sweeter than ordinary sugar so less sweetener is needed to acheive the same level of sweetness.

So even though both cans of Irn Bru have exactly the same volume of liquid in them, the normal Irn Bru has more molecules (in this case sugar) dissolved in the liquid. This means that the sugar-free Irn Bru will float and the normal Irn Bru will sink. The more dense a substance is, the closer the molecules are inside that substance.

Density can also be affected by temperature and pressure. For example in warm air, the molecules have lots of energy and bounce about in space, knocking the other molecules about. So the spaces between the molecules are quite large, and the density is very low. However, in cold air the molecules don't have much energy so they don't bounce about in space very much and the molecules stay quite close together, so cold air is more dense.

1 Whether or not things float depends on their ________.
2 What is the density of pure water?

Why is the regular can denser than the sugar-free can?

4 What are the molecules like in a dense substance?
5 How does heat affect density?
6 Are you more or less dense than water? Clue: can you float?

1 Try the Sink or Swim? experiment at home with some cans in a bucket of water. Compare pairs of diet or sugar-free drinks to regular drinks. It should work with all fizzy drink cans because all fizzy drinks are roughly the same thing, just with different flavours added. Try other kinds of cans, such as natural juices in cans.
2 Which is denser: water or oil? Pour water and cooking oil into a small clear plastic bottle then screw the top on tight. Give it a good shake then put it down and leave it to settle. The two liquids will separate out: which do you think is denser?